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U.S. airlines are getting better at many things except getting you to your destination on time.

They are losing fewer bags. Complaints are down.

And on the anniversary of a man getting dragged off a plane because a crew member needed his seat, airlines are bumping fewer passengers.

That's the upshot of a report issued by academics who analyze numbers compiled by the Transportation Department. The annual Airline Quality Rating shows that as a whole, the 12 largest U.S. airlines improved their performance last year in three of the four categories tracked — on-time performance for flights, passengers denied boarding involuntarily, mishandled bags and customer complaints.

The authors ranked Alaska Airlines first, followed closely by Delta Air Lines in a report released Monday. Budget carriers Spirit Airlines and Frontier Airlines finished at the bottom. United Airlines held on to the eighth position for the third year in a row and American Airlines remains ranked nineth.

"The industry is improving, but there are still a lot of frustrated travelers out there," said one of the researchers, Brent Bowen, dean of aviation at Embry-Riddle Aeronautical University. He blamed a lack of transparency in the ticketing process and the increase in delayed flights.

The industrywide on-time performance — never great — declined a bit last year, when 80.2 percent of flights arrived within 14 minutes of schedule, which is the government's definition of on time. That was down from 81.4 percent in 2016.

Customer service hit bottom when Chicago airport officers bloodied and dragged a 69-year-old man off a United Express plane. An airline employee had called security to go on board and make room for a crew member commuting to work. Video of the incident was played countless times online and on television.

The passenger, David Dao, reached an undisclosed settlement. United and other airlines took steps to reduce overbooking, and they worked — bumping passengers off oversold flights fell to an all-time low, just one in every 30,000 travelers.

Complaints lodged with the Transportation Department dropped too, although most aggrieved travelers complain directly to the airline — carriers don't report those numbers.

Bowen surmised that most travelers don't know how to file a complaint with the government. Even if they do, he said, their expectations for airline service "are so low now that they just want to be done with the experience and not have to reflect on it and write a complaint."

The report compiled by Embry-Riddle and Wichita State University is now in its 28th year. It once stood alone, but there are now many ratings of airlines including ones from J.D. Power and Skytrax.

Henry Harteveldt, a travel-industry analyst in San Francisco, said airlines "don't care about these reports because they don't have to care."

Mergers have left consumers with fewer choices. Many passengers stick with one airline because they belong to its frequent-flyer program. And price, not quality, is often cited as the top factor when consumers shop for flights.

"The airline that comes in first in the AQR won't pop a bottle of Champagne, and the airline that comes in last won't shed a tear," Harteveldt said.